Rate coefficients as a function of time during the after-effect of a photoinduced crosslinking polymerization

The polymerization of a dimethacrylate monomer occurring in the dark after the initiating light has been switched off (so-called after-effect) was modeled by assuming of two different termination mechanisms: monomolecular (Model 1) and bimolecular (Model 2). Time dependent monomolecular termination (k(t)(m)) and bimolecular termination (k(t)(b)) rate coefficients and a time independent propagation rate coefficient k(p) are used in the models. Both k(t)(m) and ktb are polynomial functions of time. A very important feature of the newly developed models is that free terms of polynomials correspond to values of k(t)(m) (Model 1) or k(p)[P-.](0) (Model 2) at the moment of stopping the irradiation (t(dark) = 0; [P-.](0) constitute macroradical concentrations at t(dark) = 0). Those values can be considered as describing the process during continuous irradiation. Calculations were performed for eight photoinduced polymerization processes, in which initiation had been interrupted at various degrees of double bond conversions (denoted as starting conversions). It was found that the conversion dependence of k(t)(b)[P-.](0) and k(t)(m) parameters extrapolated to t(dark) = 0 appearing in two various termination models was similar.